This application claims the priority of Korean Patent Application No. 2002-17604, filed Mar. 30, 2002, which is incorporated herein in its entirety by reference.
1. Field of the Invention
The present invention relates to an apparatus and method for driving a plasma display panel, and more particularly, to an apparatus and method for automatically adjusting a gradient of a reset ramp waveform of a plasma display panel, in order to automatically adjust a ramp waveform generated in a reset period, which is a period contributing to deviation adjustments between circuit components and between panels.
2. Description of the Related Art
In general, a plasma display panel (PDP) is a next generation flat display apparatus which indicates characters and images using plasma generated by gas discharge. In the plasma display panel, hundreds of thousands to several millions or more pixels are arranged in a matrix type based on a size of the PDP.
As shown in FIG. 1, a conventional plasma display panel driving circuit includes a scan electrode driving board 110, a plasma display panel (PDP) 120, a common electrode driving board 130, and an address driver integrated circuit (IC) 140.
A driving sequence of the PDP is divided into a reset period, a scan period and a sustain period. The reset period removes a display hysteresis by discharging all cells and simultaneously eliminating wall charges. The scan period selects a discharge cell from a matrix configuration generated by a combination of raw electrode and column electrode so that an address discharge is formed. The sustain period displays an image while repeatedly charging/discharging a discharge cell formed in the scan period using an energy recovery process.
Ramp waveforms as shown in FIGS. 2A and 2B are employed to uniform a wall charge elimination in a cell indicating a prior image signal and stabilize a wall charge generation for indicating a next image signal in the reset period.
Contrast of high quality and reliability of accurate image display discharge in the PDP are greatly affected by a gradient of the ramp waveform applied in the reset period. The ramp waveform generating circuit applied in the reset period of the PDP driving circuit has three type waveforms, that is, an X-rising ramp waveform generator 130A, a Y-rising ramp waveform generator 110C and a Y-falling ramp waveform generator 110D.
The most suitable image is displayed by changing the gradient of the ramp waveform generated in the respective ramp waveform generator based on characteristic deviation between the plasma display panels and characteristic deviation between circuit elements.
Conventionally, the gradient of the ramp waveform was manually adjusted as follows.
FIG. 3 is a detail circuit diagram of a conventional X-rising ramp waveform generator according to the prior art.
A gate driver 31 amplifies an input square wave signal X_rr_sig to supply a sufficient power on order to switch on/off a MOS field effect transistor (MOSFET) switch X31. In case of separating a source terminal of the MOSFET switch X31 from a signal ground line, a sufficient power must be supplied to switch on/off the MOSFET switch X31.
After the input square wave signal X_rr amplified by the gate driver 31 passes through a variable resistor Rg, the signal X_rr is inputted to a gate terminal of the MOSFET switch X31. If the signal X_rr is ‘ON’ (output end voltage of the gate driver is Vgg), a gate current ig flowing through a path Rg-Cgd-D2 is given by the following Equation 1:                               i          g                =                                            V              gg                        -                          V              th                                            R            g                                              (        1        )            
Herein, Vth is a threshold voltage of the MOSFET switch X31, typically about 5V. At this time, a voltage rising gradient dVgd/dt of both ends of Cgd is expressed as the following Equation 2:                                           ⅆ                                                   ⁢                          V              DG                                            ⅆ                                                   ⁢            t                          =                                            ⅆ                                                           ⁢                              V                DS                                                    ⅆ                                                           ⁢              t                                =                                                    i                g                                            C                gd                                      =                                                            V                  gg                                -                                  V                  th                                                            C                gd                                                                        (        2        )            
As seen from the above Equation 2, if the variable resistor Rg is adjusted, a voltage gradient between a drain terminal and a source terminal of the MOSFET switch X31 is changed, whereby a voltage gradient of the ramp waveform applied to both ends of the PDP can be adjusted.
If the signal X_rr is ‘OFF’, the gate current ig is drastically decreased through a path Cgs-D1. Herein, Cgs is referred to as a parasitic gate-source capacitance of the MOSFET switch X31. FIG. 4 shows a simulation result of a X rising voltage gradient of the PDP according to a change of the variable resistor Rg using Pspice. It can be seen from FIG. 4 that the gradient of the ramp waveform is reduced as the variable resistor Rg increases.
According to the prior art having the above-described circuit configuration, the gradient of the PDP reset ramp waveform was adjusted by manually adjusting the variable resistor Rg while directly watching an image which is outputted in an image adjustment process step. Thus, there are problems in that the image adjustment process is complex and an accurate image adjustment is difficult to be performed in mass production.